In industry, especially the motor vehicle industry, it is often necessary to assemble all kinds of components by adhesive bonding by means of adhesive compositions, in particular heat-curable ones.
Industrial bonding must meet a number of criteria. On the one hand, it must be quick because it is intended to be used on assembly lines at a high rate, not exceeding 5 minutes in most cases. On the other hand, the adhesive bonding must be carried out at a moderate temperature, of the order of 120.degree. C. to avoid a distortion of the components which, in general, are based on plastics.
Finally, the adhesive bonding ideally requires a "ready-for-use" adhesive composition (or single-component composition) which, furthermore, is stable for at least 1 month at a temperature lower than 25.degree. C.
Heat-curable adhesive compositions are known where adhesive bonding is concerned.
Patent Applications JP-A-071 73243 and EP-A-171 015 describe crosslinkable compositions with delayed reactivity which contain isocyanates and/or urethane prepolymers and amines partially deactivated by means of mono- or polyisocyanates.
JP-A-57 108121 describes a urethane resin intended for the preparation of moulded articles which includes a fine powder of a crosslinking agent such as dodecanediamine.
JP-A-05 032948 proposes a sealing composition based on a polyurethane which has at least one NCO functional group and on a polyamine which has at least two NH.sub.2 functional groups, dispersed in a solvent such as liquid paraffin. The solubility of the amine must remain lower than 5 g per 100 g of solution.
It has now been found that the addition of a suspension of polyamine particles of determined size to compositions based on polyurethanes enables their thermal curing to be controlled. The compositions thus obtained exhibit good adhesiveness and storage stability properties.